Gas metal arc welding (GMAW) is a welding process in which an electrical arc between a filler metal and a work piece heats the filler metal and the work and welds them together. The filler metal is usually a consumable electrode which is fed into the process as fast as it is consumed. The electrical arc is formed between the tip of the consumable electrode and the metal of the work piece. The GMAW welding process can be used to join two pieces of sheet metal together, as well as in many other applications. An example of a welding gun and an arrangement for GMAW is schematically shown in FIG. 1. A consumable welding electrode 14 is fed into the welding process through a welding gun 10. Electrode 14 is melted by an electrical arc 18 established between the electrode and the work piece consisting of metal sheets 11 and 13. The welding process is usually performed in the shielding atmosphere of externally supplied gas, such as Ar, CO2, and their mixtures, which enters the welding process through a gas nozzle 12 in welding gun 10 and shields the arc, the tip of the electrode and the pool of molten metal 15 by forming a gas shield 16. The advantages of the GMAW process is the high quality weld that can be produced faster and with very little spatter and loss of alloying elements due to the gas shield and a stable electrical arc.
Solid and metal-core wire electrodes are commonly used in gas-metal arc welding, because they produce high strength welds in a single or multi pass process at high welding speeds. Such weld wires are formulated to form a solid, nonporous weld bead with a good tensile strength, ductility and impact strength to meet the requirement of the desired end use application. Solid and metal-cored wires are also formulated to minimize slag formation, although small slag islands or a thin line of slag often remain at the weld toe in the traditional gas-metal arc welding process. The slag lines or islands have to be removed before painting or coating, otherwise they will eventually peel off after coating, exposing the metal to ambient air, facilitating corrosion and detrimentally affecting the appearance of a piece.
Solid wires are considered to be some of the most popular types of welding wires. Continuous welding made possible by solid wire leads to a higher productivity compared to shielded metal arc welding with a consumable stick electrode. Solid wires are made by drawing a hot rolled rod of a specific chemistry to a desired diameter. Solid wires are then cleaned and copper plated, if necessary. Mn and Si present in a solid wire oxidize during the welding process and produce isolated, thin slag islands. The productivity advantages of solid wires are sometimes offset by the time required to remove the slag deposits or islands that form on the surface of the weld.
Metal-core wire electrodes are increasingly used as an alternative to solid weld wires for improved productivity in structural fabrication. Metal-core weld wires are composite tubular filler metal electrodes having a metal sheath and a core containing a composition of various powdered materials. The core composition of metal-core wires includes iron powder, usually as filler material. The core composition comprises approximately 1 to 45% of the total wire weight. The iron powder content is usually considerable and comprises generally between approximately 0 and 44% of the total wire weight. During the manufacture of metal-core wires, the core composition is blended and deposited onto a steel strip, which is formed into a tube or sheath about the core composition in a forming mill. The steel sheath surrounding the core composition is then drawn through reducing dies to a specified diameter. Metal-core wires provide increased weld deposition rates and produce wider and more consistent penetration profiles than solid wires. In addition, metal-core wires generate less spatter, provide improved arc stability, and produce weld deposits with improved wetting characteristics and gap-bridging capabilities in comparison to solid wires. However, these productivity advantages which metal-core wires provide are sometimes offset by the time required to remove the slag deposits or islands which form on the surface of the weld.
When a gas-metal arc welding process with a solid wire is used for welding ferrous alloys, it is known and customary in the welding industry that the shielding gas always consists of a mixture of Ar and a certain percentage of CO2 and/or O2. The additions of active gases, such as CO2, O2, to inert noble gas Ar (and sometimes He) for gas-metal arc welding of ferrous alloys are considered to be necessary to stabilize the erratic arc, achieve better penetration and a better weld bead wetting in spite of their causing excessive welding fuming and their detrimental effect on mechanical properties of the weld. Such deterioration of mechanical properties is caused by active gases CO2 and/or O2 forming oxide inclusions in the weld metal. Silicon islands usually have to be removed from the weld surface prior to any painting or coating operation, which leaves a visible mark or scar on the weld.
The mechanical properties of the weld of ferrous alloys, as well as improvements of the welding conditions, would be desirable, if the detrimental oxidizing effect of active gases in the shielding mixture could be reduced without destabilizing the arc.